The Football Association has begun an investigation into allegations that referee Mark Clattenburg used "inappropriate language" during Chelsea's clash with Manchester United on Sunday.
The Blues lodged the complaint following their 3-2 home loss to United, with the club accusing Clattenburg of aiming a racial slur at midfielder John Obi Mikel.
Former referee Jeff Winter has defended his counterpart, but he also admitted that the issue would become "very, very serious" if racial words were spoken.
Meanwhile, it is also understood that the club have launched a complaint about words spoken to Juan Mata during the clash.
